The invention relates to a method of determining new luminance value data based on original luminance value data to be displayed on a matrix display device, where said luminance value data are coded in sub-fields, said sub-fields comprising a group of most significant sub-fields, and a group of least significant sub-fields, wherein a common value for the least significant sub-fields is determined for a set of lines.
The invention also relates to a matrix display device comprising means for determining new luminance value data based on original luminance value data to be displayed on a matrix display device in accordance with said method.
The invention may be used e.g. in plasma display panels (PDPs), plasma-addressed liquid crystal panels (PALCs), liquid crystal displays (LCDs), Polymer LED (PLEDs), Electroluminescent (EL), television sets used for personal computers, and so forth.
A matrix display device comprises a first set of data lines (rows) r1 . . . rN extending in a first direction, usually called the row direction, and a second set of data lines (columns) c1 . . . cM extending in a second direction, usually called the column direction, intersecting the first set of data lines, each intersection defining a pixel (dot).
A matrix display device further comprises means for receiving an information signal comprising information on the luminance value data of lines to be displayed and means for addressing the first set of data lines (rows r1, . . . rN) in dependence on the information signal. Luminance value data are hereinafter understood to be the grey level in the case of monochrome displays, and each of the individual levels in color (e.g. RGB) displays.
Such a display device may display a frame by addressing the first set of data lines (rows) line by line, each line (row) successively receiving the appropriate data to be displayed.
In order to reduce the time necessary for displaying a frame, a multiple line addressing method may be applied. In this method, more than one, usually two, neighboring, and preferably adjacent lines of the first set of data lines (rows) are simultaneously addressed, receiving the same data.
This so-called double-line addressing method (when two lines are simultaneously addressed) effectively allows speed-up of the display of a frame, because each frame requires less data, but at the expense of a loss of the quality with respect to the original signal, because each pair of lines receives the same data, which induces a loss of resolution and/or sharpness due to the duplication of the lines.
For the above-mentioned matrix display panel types, the generation of light cannot be modulated in intensity to create different levels of grey scale, as is the case for CRT displays. On said matrix display panel types, grey levels are created by modulating in time: for higher intensities, the duration of the light emission period is increased. The luminance data are coded in a set of sub-fields, each having an appropriate duration or weight for displaying a range of light intensities between a zero and a maximum level. The relative weight of the sub-fields may be binary (i.e. 1, 2, 4, 8, . . . ) or not. This sub-field decomposition, described here for grey scales, will also apply hereinafter to the individual colors of a color display.
In order to reduce loss of resolution, line doubling can be done for only some less significant sub-fields (LSB sub-fields). Indeed, the LSB sub-fields correspond to a less important amount of light, and partial line doubling will give less loss in resolution.
The use of partial line doubling should be effective. Only a few LSB sub-fields doubled would yield a little gain of time. Too many sub-fields doubled would yield an unacceptable loss of picture quality.
Another aspect that influences the quality is the calculation method of the new data of doubled sub-fields. Different calculation methods giving different results can be used. The method used should give the best picture quality, as seen by the observer""s eyes.
As the LSBs are doubled in partial line doubling, the value of the LSB data for two neighbouring or adjacent lines must be the same. The following methods are used for the calculation of these data:
The LSB data of odd lines is used on the adjacent even lines (simple copy of bits).
The LSB data of even lines is used on the neighbouring or adjacent odd lines (simple copy of bits).
The average LSB data of each pair of pixels is used for both new LSB values.
These methods allow a reduction of the addressing time, at the expense of a loss of resolution. However, a difference, and in some instances a large difference, may exist between the original luminance values to be displayed and the new luminance values actually displayed.
It is an object of the invention to provide a method of calculating new data to be displayed on a matrix display device, using multiple line addressing of least significant weight sub-fields, where a loss of resolution and/or sharpness with respect to the image obtained by single line addressing of all sub-fields is reduced, and preferably minimized.
To this end, a first aspect of the invention provides a method as defined in claim 1 of determining new luminance value data based on original luminance value data. In the traditional methods, the most significant sub-fields (MSB) of each line are kept as in the original data. By including the most significant sub-fields as well as the least significant sub-fields in the calculation, one broadens the set of possible solutions. This invention thereby allows better results.
The invention provides a method which is applicable to both binary and non-binary sub-fields.
Specific embodiments of this method are defined in the dependent claims 2 to 11.
Claims 3, 4 and 5 disclose embodiments which are applicable to both binary sub-fields. These methods are easy to program.
Claims 6 to 9 disclose embodiments which are applicable to both binary and non-binary sub-fields.
Claims 10 to 14 disclose simplified versions which are applicable to both binary and non-binary sub-fields, and, although simplified and easy to implement, having good practical results.
A matrix display device is defined in claim 15.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiment(s) described hereinafter with reference to the accompanying drawings.